No. You need to complete the year. the 13 month bonus is a sure fire way to keep people till the end of the year at the very least.

by doing so, they are bracing themselves for attrition in the month of march.

why ?

People wait till december only they think about tendering.

then they think, ah shit. jan / feb is new year and cny. so they wont tender also

in the end they tender and leave also probably march.